1. Field of Invention
This invention relates in general to antenna beam-forming, and more particularly, to a transmit/receive module architecture for a beam-forming antenna array.
2. Related Art
Active phased array antenna systems and/or active aperture array antenna systems (generally known as “active antenna arrays”) have become more common place with the advent of individual solid-state transmit/receive (T/R) microwave module element (known as “T/R modules”), thus avoiding the distribution and phase shifter losses generally encountered in the passive array antennas. As such, the performance of modern radar systems with active antenna arrays is mainly driven by the performance of these T/R modules. In general, for the same radiated power, active antenna arrays have been found to be more efficient, smaller and lighter than conventional passive array antenna systems. Due to the close connection of the T/R modules to the radiating elements, the losses in both cases (i.e., transmit and receive losses) are low, compared to the passive array systems. This generally leads to a low received noise-figure and high transmit efficiency. Furthermore, active antenna array techniques may help satisfy the need to generate large amounts of power for long-range surveillance and tracking radar systems. Moreover, active antenna arrays allow for low sidelobe level control on the radar receive mode, adaptive null placement to minimize jamming, and beam forming and steering applications. In summary, the functions of a T/R module include generation of transmit power, low noise amplification of received signals coupled to and received from the respective radiating element, phase shift in transmit and receive modes for beam forming and/or steering, and variable gain setting for aperture weighing during reception. It is appreciated by those skilled in the art that depending upon the design requirements, a typical beam-forming antenna array may include thousands of T/R modules.
Unfortunately, cost is always an issue for a resulting complex of a large number of T/R modules. In addition, microwave plumbing is required both to supply the microwave radio frequency (“RF”) signal to be transmitted to each T/R module and to receive microwave RF signals from the T/R modules once an incoming signal has been received. In the receiving case, the received signal from the various T/R modules is typically combined in a microwave transmission network and presented as composite signal to a baseband or intermediate frequency (“IF”) processing stage. For example, consider a radar phased array antenna 100 shown in FIG. 1. As is known in the art, this radar phased array antenna 100 may be utilized to track N multiple targets such as, for example, targets 102, 104, 106, and 108 (it is appreciated that only four targets are shown for simplicity) with N individual antenna beams such as beams 110, 112, 114, and 116, respectively. Each target produces a particular spectral return depending upon its Doppler and range properties relative to the radar phased array antenna 100. As an example in FIG. 2, the first target 102 may produce a first target spectrum 200 versus offset frequency, the second target 104 may produce a second target spectrum 202 versus offset frequency, the third target 102 may produce a third target spectrum 204 versus offset frequency, the fourth target 104 may produce a second target spectrum 206 versus offset frequency. The resulting combined spectrum signal 208 will contain these various spectral returns.
Unfortunately, although T/R modules have improved the efficiency and cost of active antenna arrays, there are several still significant drawbacks involved in processing the combined spectrum signal 208 shown in FIG. 2 resulting from an active antenna array. For example, one drawback is that there is insertion loss from each T/R module to a received signal network (not shown) that may include a plurality of associated RF combiners and couplers. In addition, it is difficult to precisely match the phase of the received signals and/or their amplitudes between individual T/R modules. Moreover, impedance matching of the T/R modules to the microwave transmission and/or reception network is typically a formidable task. Moreover, the receiver noise-floor tends to degrade as the various received RF signals from the T/R modules are combined in the microwave transmission network. In addition, the combination of the various received RF signals generally tends to degrade the desirable ability to sector an active antenna array so as to track multiple targets.
Therefore there is a need for an improved active antenna array using a T/R architecture that is capable of overcoming the problems discussed above.